He will been forever stuck between the two worlds, the good and the evil, without entering either or leaving either behind. Which of the underlined word is grammatically incorrect?

My favorite band ____ a concert on September, 15. My sister have bought me a ticket for the concert. I____ go to the concert together with my sister. ___ you join us?

John has saved a lot of money. He____ a new computer game.

They are going to Europe next break. The sentence means that they have already had ___ plan.

My older sister, Kirana, will ___ me a new bike if I top my class this semester.

My sister and her friends ___ on a trip the day after tomorrow.